'Shouldn't' be, as they're the same drivers etc, though no doubts some software parts underneath are still evolving. With those symptoms on a 680, I'd first be making sure to keep GPU temps below 70C & kick up the voltage [& fan]. Also dpc's (software interupts) have a fixed additional latency on win8 supposedly, due to some or another changes in (kernel) timers, so I'd suggest trying the latest beta driver & check other drivers in the system such as sound, USB & wifi don't have quality/dpc issues ( http://www.thesycon.de/eng/latency_check.shtml , note that it'll supposedly run on windows 8, but incorrectly show added 1ms latency ) Under newer models a single poor quality driver could be causing timeouts, and win8 ones in general are sure to be less mature (That goes for chipset, usb, pretty much everything).
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"It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is the most adaptable to change."
Charles Darwin